Process of color analysis and color synthesis for the projection of colored pictures in photography and cinematography



Oct. 7, 1941. FERRlGu'ro r-:TAL 2,258,380 PROCESS 0F COLOR ANALYSIS `AND COLOR SYNTHESIS. FOR THE PROJECTION OF COLORED PICTURES IN PHOTOGRAPHY AND CINEMATOGRAFHY Patented Oct. y 7, 1941 l SYNTHESIS FOB THE PROJECTION F COLORED PICTURES IN PHOTOGRAP CINEMA AND TOGBAPHY Italo Ferriguto and Alessandro Moauro', Rome, Italy Application september 19, 193s, semi No. 230,118

, In Italy August 22, 1938 1Claim. (CLSB-16.4)

In the investigation of the anatomical and histologicalv foundations of the three-color theory, the actions upon the 'retina which determine color-vision-have been revealed and it was found that the three basic physiological sensations were evoked by specic stimuli, the physical value of which diilers considerably from that hitherto as- Sum-ed. v l

In practice, these investigations have led to fundamental rules which in all processes of direct or indirect,l optical or mechanical colorreproduction, by the prism, lens or other screen -method, on the basis of the three or two-color selection of the pictures, furnish the exact elements for' the color analysis and for the color synthesis according to the addition principle.

At the present time, the analysis is obtained by the insertion of filters in front of the objective. These filters allow the production of monochromatic partial color components, that is to say the orange-colored, green and violet parts of the object are taken separately with almost complete neglect ot the natural shading-eiect of the object.

The process according to the invention replaces the said monochromatic partial color components by photographicv partial pictures, which all show an almost complete shadingof the object takemand in which moreover: the green partial picture is isopanchromatic, that is to say it produces in black and white the physiological 'r These improvementslead to soft and harmonivous color effects, which do not hurt the eye even inthe special conditions of accommodation in semi-dark projection rooms. -Moreover, the shading of the pictures remains perfectly true, that is to say the colors fade away in 'the 4shadows according to the strength of the light, without however altering their tone.

Fig. 1 illustrates 'diagrammatically the preparation of the negative of a two-color film.

Fig. 2 illustrates diagrammatically the preparation of the negative of a three-colorrlm.

Fig. 3 illustrates diagrammaticaly the projection of the positive of a two-color film.

Fig. 4 illustrates diagrammaticallyfthe projec- 'tion of the positive of a three-color' film.

lFor the normal applications, for which the process according to the invention is intended,v

viz. scientiiic or documentary pictures of topographical and photogrammetrical nature, photographic surveying records, artistic and docu- 'mentary illms` and so on, the separate photographic partial pictures must be produced with regard to the following practical rules:

(1) Using one and the sameemulsion for all pictures. the ones to be'selected from `all the emulsions to be found in the trade being those which are sensitive to red upto the limits of the light-value of all color-tones of the object; vthe l orange-colored partial picturepossesses in the positive as compared with the isopanchromatic partial picture a progressively decreased density in all the areas corresponding tothe red. 'orangecoxcred and yeucw` parts of the object, but an approximately equal density in the areas corresponding to the greenish-yellow, and a progressively increased density in the areas corresponding to the green, blue and violet ofthe object; the violet partial picture in the positive as compared with the isopanchroxnatic partial picture a progressively decreased density in the areas corresponding to the` blue, red and violet parts of the object, and a progressively increased'density in the areas corresponding to the orange-colored, yellow and green parts of the object.

visible spectrum.

(2) Taking the isopanchromatic partial picture through a filter which corresponds to the one supplied by the manufacturer for the normalising of the emulsion employed (for example, the Agfa green nlter 'l0 or 'Il for natural or articiallight). The use of this lter is necessary because .the panchromatic emulsions at present on sale show a sensitivity dinering from the sensitivity ol the eye, and therefore without a correcting filter they cannot produce isopanchromatic pictures. s

(3) Using an orange-yellow or purple-colored filter.y for the taking of the second or third partial pictures. These filters must determine for the selected panchromatic emulsion a coemcient Consequently, tothe invcnim. Bgm

actual color selection takes place, but the rela-4 tive light and kdark eect or shading of the individual partial picture is modulated according to the color and the brightness oi' the difierent parts of the' object taken.

v ofthe lengthening of the time exposure which is equal to that of the notmalising filter employed for the isopanchromatic partial picture.

This last rule, which is an empirical assumption. is `nevertheless accurate, because it proportions the selective power of the filtery to the time necessary for the exposure ofk a. photographic material of a given sensitivity andwith a given illter color.

The exact color ot the orange-yellow or purple- 66 colored filter must however harmonise' with the quality of the incoming light, that is to say either with natural light or with the various artiilcial light sources.

For the color synthesis, the three monochrome colored or filtered partial pictures, in greenishblue, orange-yellow and purple-violet, must be added together on the projection screen by suitable optical, mechanical or physiological means.

The process is applicable with the observance of the same rules to photographic material with multicolor screens (autochromatic material) and to the various optical arrangements for prism or lens screen lms.

In cases where for the obtaining of artistic or special scemo-graphical effects or in the film treatment elements of a personal chromatic interpretation are to be introduced with facility, then the operation is advantageously carried out according to the two-color system with the use of one isochromatic photographic picture and one picture taken through an orange-red lter. The reproduction of color is then not quite correct but the colors themselves can be modified at will by alteration of the filter at the projection stage. The inaccuracies are far less serious than those which arise in the processes at present employed so that the method according to the invention can certainly find application for most kinds of artistic lms.

The alternate production of three-color pictures truev to nature and artistic two-color pictures may often be desirable. In this case the procedure is carried out substantially according to the following scheme, given by way of example:

By means of suitable optical or mechanical devices, two pictures of reduced size are formed simultaneously or in rapid sequence upon the lm section reaching an ordinary photogram, one of these pictures having always to be isopanchromatic.

The second picture of reduced size must be of the described orange-red typein case it is a question of the production of two color picturesfor the Whole series of exposure.

If, on the other hand, it is a question .of the production of three-color pictures, then each photogram must have its isopanchromatic picture associated alternately with an orange-yellow and a purple-colored picture. In the Dositi've, each picture is dyed to the appropriate color.

The projection takes places with a normal apparatus in such a way that at the picture aper ture there always appear two pictures-ot reduced there will be obtained two incomplete co1or syntheses for every' two photograms, which will however be combined chromatically by addition upon the retina.

Among the advantages of the process according to the invention there is especially to be named the fact that the color eiect is obtained without raising the cost of cinematographic production.

What we claim is:

In a method of three-color photography of the kind in which on different portions of a single light sensitive surface are produced three differently selected component images, the step of producing on the panchromatic emulsion, through a iilter rectifying the specidc sensitivity of the panchromatic emulsion used so as to reproduce in black and white the physioloirical light intensity of all the chromatical tones oi the original, an isopanchromatical negative, and through an orange-yellow and through a purple filter two color selected negatives, the step of producing positives of the said negatives and the` step of projecting, in superimposition on a screen, pairs of positives comprising alternatively an isopanchromatical positive together with an orange-yellow component positive, and an isopanchromatical positive together with a purple component positive, the said positives being projected through colored filters and precisely the isopanchromatical positive through a green filter, the orange-yellow component positive through an orange filter and the purple component image through a violet filter, the two different pairs of optically superimposed component imagesbeing added on the retina in consequence oi their rapid succession on the screen.

ITALO FERRIGUTO.

ALESSANDRO MOAURO. 

